In medical ultrasound imaging systems using a pulse-echo method, the image quality typically depends on the lateral and axial resolution of the imaging beam. The axial resolution is mainly determined by the pulse length, which in turn is mainly determined by the center frequency and bandwidth of the ultrasound imaging device. The lateral resolution is mainly dependent on the aperture size, center frequency and bandwidth of the imaging device. The ultrasound imaging device is typically a single element transducer or transducer array.
For a well focused ultrasound transducer, the beam width (β) at a focal point is β=f#λ, where f# is the ratio of the focal depth to the diameter of the aperture and λ is the wavelength of the pulse. Thus, an increase in aperture size can allow a narrow beam width to be achieved over a wider range of focal depths. For example, in intracardiac echocardiography (ICE) imaging applications, the target tissue to be imaged could be on the order of 10 centimeters (cm) from the imaging device. Typically, the imaging device must be routed through an artery or other narrow body lumen in order to place the imaging device into proximity with the target tissue. If the desired resolution is one millimeter (mm) and a 10 Megahertz (Mhz) ultrasound frequency is used, the necessary aperture size would be over 10 mm. Conventional imaging devices having an aperture of this magnitude are too large to be delivered into a living being through a catheter and the like.
Accordingly, improved systems and methods are needed, which allow the interior of a living being to be imaged with imaging devices having large apertures.